1. Field of the Invention
This invention relates to a process for the construction of electrodes for use in an electrochemical device.
2. Description of the Prior Art
The advantages of lightweight electrodes for use in fuel cells have been recognized. These electrodes essentially comprise an admixture of electrocatalyst and hydrophobic binder deposited on a substrate material such as a porous carbon or metal support, wire mesh or grid. The electrodes are extremely thin, having low internal electrical resistance and furthermore, take up only limited space permitting the construction of highly compact cells having a high energy to volume and energy to weight ratio. One difficulty with these electrodes, however, is obtaining a controlled distribution of electrocatalyst particles with the hydrophobic polymer particles throughout the electrode structure. The performance of polytetrafluoroethylene (PTFE) bonded platinum black and platinum supported on carbon fuel cell electrodes is limited by the size of the effective catalyst clusters interspersed in the porous gas diffusion electrode structure. The effective size of the catalyst clusters (i.e., "agglomerates") between the gas diffusion channels maintained by the dispersed PTFE is usually large; therefore, utilization of the catalyst in the interior of the electrolyte filled catalyst agglomerate requires the molecules of gaseous reactant to travel a long diffusion path.
Conventional methods for dispersing the electrocatalyst particles, such as fluid energy milling, ball milling, ultrasonic agitation, and the addition of non-ionic surfactants, have been generally unsuccessful in sufficiently reducing the effective catalyst agglomerate size, so that the catalyst agglomerate in prior art fuel cell electrode structures ranges between 1.times.10.sup.-6 and 20.times.10.sup.-6 m. This is considered too large.